President Barack Obama speaking during the opening ceremony for the National September 11 Memorial Museum. (Photo: John Angelillo-Pool/Getty Images)

President Barack Obama told the story of “the man in the red bandana,” who spent his final moments leading men and women trapped in the South Tower of the World Trade Center to safety on September 11, 2001.

“In those awful moments after the South Tower was hit, some of the injured huddled in the wreckage of the 78th floor. The fires were spreading. The air was filled with smoke. It was dark, and they could barely see. It seemed as if there was no way out. And then there came a voice–clear, calm, saying he had found the stairs. A young man in his 20s, strong, emerged from the smoke, and over his nose and his mouth he wore a red handkerchief,” said the president.

“He tended to the wounded. He led those survivors down the stairs to safety, and carried a woman on his shoulders down 17 flights. Then he went back. Back up all those flights. Then back down again, bringing more wounded to safety. Until that moment when the tower fell.”

One of Welles Crowther’s red handkerchiefs is now on display at the National September 11 Memorial Museum, where leaders gathered this morning for a moving ceremony to commemorate its opening more than a decade after the terror attacks.

“From this day forward, all those who come here will have a chance to know the sacrifice of a young man who–like so many–gave his life so others might live,” the president said.

Later in the ceremony, Mayor Bill de Blasio spoke about the “Survivors’ Staircase”–the last 28 steps of a narrow outdoor staircase that lead some of the last survivors to freedom on Vesey Street.

“Today, when you walk down the museum’s last set of stairs that lead to bedrock, whether you walk slowly down the wide elegant staircase, or stand comfortably on the moving escalator, you will travel right beside the Vesey Street staircase,” he said. “And as you do, imagine for a moment that these hard concrete stairs were once, for hundreds of people, the last and long-sought path to survival.”

Gov. Andrew Cuomo honored those who took down Flight 93 before it got to Washington, D.C., while New Jersey Gov. Chris Christie talked about the international response to the tragedy. Former Mayor Rudy Guliani honored first responders, and former Mayor Michael Bloomberg, who championed and helped to finance the museum’s construction, focused on the lessons of the tragedy.

“The stories are the proof that what we do and the choices we make affect each others’ lives and the course of human history,” said the former mayor, who told the audience he hoped those who visited the site would “come away with a sense, not of the worst of humanity, but the best.”

“This museum is a testament to the resilience, the courage and the compassion of the human spirit,” he said.

Before the ceremony, Mr. Bloomberg led the president, First Lady Michelle Obama, former President Bill Clinton and former Secretary of State Hillary Clinton on a tour of the museum, walking past a massive rusted antenna and elevator motor from the north tower a Ladder 3 fire truck, which had been badly damaged in the attacks.

After the ceremony, Mr. Clinton raved about the museum, which he said had far exceeded his expectations.

“I thought it was a magnificent ceremony. Its a stunning museum,” he told reporters. “They did a brilliant job …. New Yorkers should be very proud of this and I hope every American gets to come and see it.”